Small-Angle Scattering of Synchrotron Radiation for Studying Solid State and Biological Systems

Abstract

Small-angle scattering of X-rays (or neutrons) allows the study of structures with sizes from 1 to 100 nm, and the applications range from biology to materials science. Traditionally, the technique has been applied to stuctural analysis in two very different ways. The first, crystallographic small-angle diffraction, is used to study the periodic arrangement of atoms, molecules, or groups of molecules. In this case one has to interpret sharp Bragg peaks occurring at small scattering angles. This technique, which relates to crystallography, shall not be discussed here. The second way, which is the subject of this paper, consists in the interpretation of the broad, diffuse small-angle scattering containing information on size, shape, and orientation of inhomogeneities (like precipitates, pores, macromolecules in solution, etc.) with sizes ranging from 1 to ≈100 nm. Such kind of information may, in principle, also be obtained by electron microscopy. The advantage of small-angle scattering is the fact that the obtained parameters (size, shape, orientation, etc.) represent average values over macroscopic sample regions, whereas the advantage of electron microscopy is the possibility to image individual objects. Small-angle scattering has been introduced mainly by Guinier [1] and by Kratky and Porod [2]. The principles of the method are reviewed in several textbooks [3-5]. In recent years, the availability of strong X-ray source as well as position-sensitive detectors has increased the potential of the technique and with the use of synchrotron radiation new applications (like, e.g., anomalous scattering, time-resolved studies, three-dimensional reconstruction of anisotropic scattering)